Presently in North America armored vehicles are engineered and manufactured primarily to provide protection against ballistic attack. The armor typically comprises a single plate, and is held in place using mechanical fasteners and/or by welding. Ballistic protection is achieved either by overlapping of several armor plates, or by covering joints with additional plates. From a mechanical strength standpoint, these armor materials are basically parasitic and do not add any significant strength to the vehicle.
More recent advances in armor materials include the use of dual hard steel. The dual property hardness steel armor has several distinct advantages over earlier prior art armor; such advantages include having requirements conducive to unlimited production quantities using existing facilities and having fabricability and intrinsic properties of steel. The earlier concept for dual property steel armor was developed from the knowledge that a high hardness was needed to shatter steel armor piercing projectiles and a high toughness was required to achieve multiple strike integrity.
Although the dual property steel armor principle provides an alloy capable of breaking up the projectile, numerous tested alloys have resulted in panel shattering. When panel shattering occurs the effectiveness of the armor is lost, particularly as an armor suitable for a multiple strike capability.
A further development of armor materials is described in U.S. Pat. No. 3,694,174, which issued on Sep. 26, 1972. That patent discloses a composite material having an outer high hardness impact layer capable of breaking up a projectile, and a lower hardness tough backing layer capable of stopping the broken up projectile. The layers are hot-rolled together to form the composite. The difference in hardness being described as being in the range of 5-8 Rockwell C. The outer layer is further described as having a Rockwell C hardness of 58-59, and the inner layer having a Rockwell C hardness of 52-53. The thickness of the layers is described as being in the range of 2-3.5 inches.
It is apparent that both layers of this material are still relatively hard. Moreover, it is unlikely that the small relative difference in hardness between the two layers would be sufficient to achieve much of a difference in mechanical properties. Further, the hot-rolling process is bound to have an adverse impact upon such properties. Also, a composite of the described dimensions would add considerable weight to a vehicle. It will be appreciated that added weight will affect vehicle performance, particularly the power and handling requirements.
It is also known, for example, from U.S. Pat. No. 4,948,673 issued Aug. 14, 1990, to employ sintered ceramic tiles e.g. based on alumina or silica, to break up armor-piercing projectiles. The broken pieces of the projectile are then stopped by an armor plate backing.